An intensive investigation of oxygen-dependent unsaturated fatty acid and hydroxy fatty acid biosynthesis is being undertaken using several species of bacilli as well as other bacteria as experimental organisms. It is hoped this study will elucidate the following: 1. The mechanisms by which temperature, oxygen and other environmental factors control or affect the rate of unsaturated fatty acid biosynthesis. 2. The mechanism of hydrogen removal in desaturation and the factors which control positional specificity in desaturation and hydroxylation of fatty acids. 3. The specific roles of oxygen in desaturation and hydroxylation reactions.